Bailey INFI 90 INPPR01 Instruction

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Bailey INFI 90 INPPR01 Instruction Manual pdf 18 page image

DESCRIPTION AND OPERATIONDATA INTEGRITY2 - 2 I-E96-624A®DATA INTEGRITYVerification of data integrity consists of even parity checkingand the checksum in each command and reply format. Theinterface retries a transaction whenever it detects a communi-cation error.There are two levels of communication breakdown detection.The first level detects a complete failure of the communicationlink. Should this occur, Function Code 130 output block onewill be set (logic one) and the alarm status bit set if port 1 fails.If port 0 fails, the output of block two will be set (logic one) andthe alarm status bit set.The second level of communication failure concerns the loss ofa single remote interface. If this occurs, all blocks coming fromthat remote interface are bad quality. The PPR makes use of auser-configurable watchdog timer or absolute retry count indetermining the sensitivity to these failures (refer toI-E93-200-20 for information about Function Code 130, S10and S12).TIMING INTERVALThe local interface attempts communication twice a secondwith all the remote interfaces. Each successful transactionresets the communication watchdog timer. Therefore, if thecommunication link is faulty, no transactions occur success-fully. After the watchdog time period expires, the link ismarked bad.For all communication transactions, the watchdog timer isreset on the reception of each character. If the time intervalbetween characters in a transaction exceeds 1.25 seconds, thetransaction is flushed and the remote interface is marked asbeing suspect. This condition causes retry logic to begin. Retrylogic consists of retrying communication once per second for anumber of times equal to one-fourth the watchdog time periodif the absolute retry count is set to zero. A non-zero absoluteretry count causes a specific number of retries (the number ofthe retry count). If the failure persists after the retry periodexpires, the remote interface is internally marked off-line andthe quality of all the points it provides are marked bad.Thereafter, a single retry of the failed remote interface occursat a period equal to one half the watchdog timer period until asuccessful transaction occurs. The local interface sets thequality of all the points to their original state (before the com-munication failure). It also does a one time poll of the currentvalue of each point.A user-configurable time delay envelopes each command/replysequence. This time delay accommodates the keying up/down